1. Field
The present invention relates to rotatable friction clutches and more particularly to improved retracting means therefor.
Rotatable friction clutches may include an axially movable pressure plate which is normally urged in an engaging direction by means of a spring arrangement and which is movable in an opposite or releasing direction by an arrangement of retracting levers in cooperation with an operating linkage. It is desirable that the ends of the retracting levers occupy a common plane normal to the axis of rotation such that the several levers share the load imposed by the operating linkage, and it is further desirable that the plane occupied by the ends of the levers be axially adjustable so that the pressure plate will be free from dragging engagement with the friction plate when the clutch is released.
The manufacturing tolerances of the various components of a clutch may result in differing axial locations for the lever ends upon initial assembly. Where the ends of the levers are not in a plane perpendicular to the axis of the chuck, release of the clutch results in uneven movement of the pressure plate causing the pressure plate to drag on the friction plate. In addition, rotation of the clutch may impose centrifugal forces on the levers which tend to pivot the lever ends from a desired axial location.
2. Prior Art
In the prior art, it is known to provide springs in the mounting structure for the levers which deflect to account for minor variations in lever position due to manufacturing tolerances. It is known also to provide levers which are inherently resilient such that differences in lever position are taken up by deflection of the lever itself. Where rigid levers are employed, it has been known to provide radially adjustable stops in the lever mounting structure which can be adjusted to bring the several lever ends into a common plane. A further solution in the prior art is the use of axial shims in the lever mounting structure by which the levers are pivoted to bring the several lever ends into a common axial plane. It is also known to provide auxiliary spring members associated with retracting levers which serve to prevent the levers from radial displacement toward the axis of the clutch.